Tissue and cell-specific antigens in chromatin from cultured rat Sertoli cells

Abstract

Cell-specific chromatin antigens have been detected in rat Sertoli cells. Antisera were raised in rabbits to dehistonized chromatin prepared from 5- to 6-day cultures of rat Sertoli cells and immunoreactivity was assessed with microcomplement fixation tests or immunoidentification of antigens separated electrophoretically and transferred to nitrocellulose sheets. Tissue specificity was confirmed further by immunoabsorption. These antisera recognized only components of Sertoli cell chromatin; chromatins prepared from rat liver, kidney, thymus, Novikoff hepatoma, a testes germinal cell fraction, or purified rat DNA showed little or no immunoreactivity. Nitrocellulose transfers of total chromosomal proteins revealed the presence of two high-molecular-weight antigens (greater than 200,000) and a broad range of weaker immunologic species ( M r about 50,000–200,000) in Sertoli cell chromatin but not liver or thymus chromatin. Deproteinization of Sertoli cell chromatin with concentrated salt and urea at pH 6 or 8 produced an increase in complement-fixing activity of the fraction sedimenting with DNA and micrococcal nuclease digestion studies showed these fractions to depend in part on DNA for antigenicity. Individual antigens in the protein-DNA pellets of pH 8 salt and urea fractionated chromatin could not be identified with antigens on nitro-cellulose sheets. Collectively, these observations suggest that at least two groups of cell-specific antigens exist in Sertoli cell chromatin; one group is detected after electrophoretic separation and transfer to nitrocellulose and the other group, reactive in complement fixation, cannot be detected through this method, apparently becoming antigenically inactive once the complex of protein and DNA is dissociated.